Answer :
First, let's expand the expression and reduce like terms:
[tex]\begin{gathered} (x-5)^2-4=0 \\ \rightarrow x^2-10x+25-4=0 \\ \rightarrow x^2-10x+21=0 \end{gathered}[/tex]Now, let's factor the new expression completely:
[tex](x-3)(x-7)=0[/tex]Thereby, the correct answer is option C